Extended Streamflow Guidance
Issued by NWS Middle Atlantic RFC

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Winter/Spring River Flood Potential Outlook
National Weather Service Middle Atlantic River Forecast Center
(MARFC)
State College, PA
9:25 am EST Thu, Feb 07, 2019


Outlook Number 19-03 - February 07, 2019

This Winter/Spring River Flood Potential Outlook is valid for the two-
week period February 7-21, 2019.

This outlook estimates the potential for river flooding (not flash
flooding) to develop during the next two weeks across the Middle
Atlantic River Forecast Center`s (MARFC) area of responsibility (Mid-
Atlantic Region) based on a current assessment of
hydrometeorological factors which can contribute to river flooding.
Across the MARFC area these factors include future weather
conditions, recent precipitation, soil moisture, snow cover and snow
water equivalent, river ice, streamflow, and others.  This outlook does
not address the severity/extent of any future river flooding.

Remember, in the Mid-Atlantic region heavy rainfall is the primary
factor which leads to river flooding.  Heavy rainfall can rapidly cause
river flooding any time of the year, even when overall river flood
potential is considered to be low or below average.

TWO-WEEK RIVER FLOOD POTENTIAL - GENERALLY ABOVE
AVERAGE

Wet soils, high streamflow, and a weather pattern that favors above-
average precipitation during the next two-week period all add up to a
generally above-average river flood potential across most of the
MARFC region.  Factors which contribute to this assessment of river
flood potential are discussed in some detail below.

CURRENT FLOODING - NONE

There is currently no river flooding occurring within the MARFC service
area.

RECENT PRECIPITATION - VARIABLE

During the last 30 days (January 7 - February 5, 2019) observed
precipitation has been quite variable across the MARFC service area.
The northern third of the region (NY, northern PA, northwestern NJ)
has recorded above to much-above normal precipitation.  Further
south, the central third of the region (southern PA, most of NJ, central
MD, northeastern WV and northern VA) has, in general, received near-
normal precipitation during the last 30 days.  Finally, the southern third
of the region (western MD, most of VA, and central portions of the
Delmarva Peninsula) has generally seen below average precipitation.
To view precipitation departure data please visit
https://www.weather.gov/marfc/Precipitation_Departures.

SNOW CONDITIONS - AVERAGE TO BELOW AVERAGE

Presently within the MARFC service area snow covers the ground
generally north and west of a line that extends from roughly Port
Jervis, NY/Matamoras, PA to near Cumberland, MD to near Elkins,
WV.  The greatest snow depths of about 3-14 inches are found in the
Chenango, North Branch Susquehanna and Upper Delaware River
Basins in NY.  From here, depths decrease gradually heading
southward to just a couple or few inches across central PA, western
MD and northeastern WV.  Snow water equivalent values range from
about 0.75-2.00 inches across the Chenango, North Branch
Susquehanna and Upper Delaware Basins in NY.  The remaining
snowpack in NY, PA, MD and WV has snow water equivalent values of
generally less than an inch.  Snow conditions are somewhat below
average for the date across about the northwestern half of the MARFC
region, where water equivalent values of 1-4 inches are more typical
for this time of year.  Elsewhere, the current lack of snow across the
southeastern half of the region is about average for early February.
Snow information can be found at
https://www.weather.gov/marfc/Snow and
https://www.nohrsc.noaa.gov.

RIVER ICE - BELOW AVERAGE TO AVERAGE

Recent observations from ice observers, along with recent satellite
photos, confirm that river ice continues to be observed along sections
of some streams and rivers, mainly across northern portions of the
MARFC region.  Where river ice exists, the river ice is not particularly
widespread or thick for early February.  As such, river ice conditions
are generally somewhat below average for early February across the
north.  Meanwhile, across about the southern half of the region, little if
any river ice is being observed which is about normal.

STREAMFLOW CONDITIONS - MOSTLY ABOVE MEDIAN

The latest data from the United States Geological Survey (USGS)
indicate above normal to much-above normal streamflow conditions
continue across much of the MARFC region.  Some scattered areas,
including southeastern VA and lower portions of the Delmarva
Peninsula, have streamflow conditions that are about median for the
date.  Some gages across the north are still being affected by ice.
Please visit https://waterdata.usgs.gov/nwis/rt for current streamflow
data.

SOIL MOISTURE CONDITIONS - GENERALLY MUCH-ABOVE
AVERAGE

The long-term Palmer drought severity index is useful to estimate deep
soil moisture conditions.  The February 02, 2019 chart (found at
https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/regional_
monitoring/palmer.gif) suggests deep soils across most of the MARFC
service area contain moisture that continues to be much-above normal
for this time of year.  Additional more detailed soil moisture information
supports the idea that soils are extremely wet across nearly all of the
MARFC area.  Go to
https://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/ and then
click on U.S. Monitoring to view this soil moisture information.

GROUNDWATER - ABOVE NORMAL TO EXTREMELY HIGH

Throughout the MARFC area, most USGS groundwater monitoring
wells continue to measure above normal to extremely high
groundwater levels.  Please visit https://groundwaterwatch.usgs.gov.

RESERVOIR CONDITIONS - AVERAGE TO ABOVE AVERAGE

Most major reservoirs within the MARFC region are holding storages
that are average to above average for this time of year.

FUTURE WEATHER CONDITIONS - GENERALLY MILD AND WET

The next week, and possibly beyond, is suggestive of a fairly wet and
generally mild weather pattern.  During the next 24 hours periods of
light-moderate rain will continue across the region until a cold front
pushes through Thursday night/Friday morning.  The heaviest rainfall
is expected across the northern half of the MARFC service area, where
additional rainfall of 0.25-1.00 inches is possible through 7am EST
Friday.  This rain/snowmelt event could result in some scattered,
mostly minor flooding to develop within the Susquehanna River Basin
in NY and northern PA during the next couple of days.  After a dry but
chilly weekend, another precipitation event begins Sunday night and
persists into Tuesday night, bringing rain to the south and mixed
precipitation to the north.  Amounts could be moderate-heavy with this
event.  A third event is possible toward the end of next week.  The
latest (February 6, 2019) longer-range weather outlook issued by the
NWS Climate Prediction Center suggests the second week of this two-
week period may see above-normal precipitation continue and have
normal or above normal temperatures.  Long-range outlooks can be
viewed at https://www.cpc.ncep.noaa.gov/.

ENSEMBLE RIVER FORECASTS - SOME THREAT OF RIVER
FLOODING DEVELOPING

The most recent runs (February 7, 2019) of the short-term (one week)
ensemble river forecasts, which take into account anticipated future
weather conditions including precipitation and temperatures, show
some mostly minor flooding is possible during the next 2-3 days across
mainly northern portions of the MARFC service area.  Beyond the next
2-3 days, longer-range ensemble river forecasts also show an elevated
risk of river flooding, compared to normal, for the next 30 days.  This
elevated risk reflects the very wet soils and high streamflow conditions
that currently exist across the region.  Please visit
https://www.weather.gov/erh/mmefs for short-term ensemble river
forecasts.

SUMMARY

Scattered river flooding, mostly minor, is possible during the next 2-3
days, mainly across northern portions of the MARFC service area.
This is due to the rain/snowmelt event expected to continue through
tonight across the north.  Beyond this event, additional significant
precipitation events seem possible during this outlook period, one next
Monday-Tuesday and another toward the end of next week.  The
anticipated wet weather pattern (and snowmelt where snow exists)
combined with very wet soils and high streamflow conditions lead to a
generally above-average river flood potential across most of the
MARFC region during this two-week outlook period ending February
21, 2019.  The latest long-range weather outlook issued by the NWS
Climate Prediction Center can be seen at
https://www.cpc.ncep.noaa.gov/.

WATER SUPPLY OUTLOOK

According to the latest (January 31, 2019) U.S. Drought monitor
(https://droughtmonitor.unl.edu), there are currently no drought
conditions within the MARFC service area.  Visit
https://www.drought.gov, https://www.cpc.ncep.noaa.gov and
https://www.weather.gov/marfc/wro_north for additional drought and
water supply information.  Assuming near-normal precipitation for the
next few months, no water supply shortages are anticipated anywhere
within the MARFC region through at least April, 2019.


Please visit the NWS MARFC homepage at
https://www.weather.gov/marfc or find us on Facebook at
https://www.facebook.com/nwsmarfc/?REF=aymt_homepage_panel
and on Twitter@nwsmarfc.

The next Winter/Spring Flood Outlook will be issued by this office in
two weeks, on or about February 20-21, 2019.

SK


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